This invention relates to the main distribution frame used in telephone systems and, more particularly, to an electric circuit and adapter for connection with individual pairs of telephone lines at the sites of their respective lightning or surge protectors.
Telephone systems throughout the United States and in other countries provide for the interconnection of the telephone lines of the subscribers at a wiring support structure known as a main distribution frame (MDF). Such frames support blocks of wire contacts oriented in a vertical attitude and in a horizontal attitude. The terminal blocks having the vertical attitude connect with the pairs of wires (Tip and Ring) which, in turn, connect with the homes and businesses of the subscribers. The horizontal terminal blocks connect with wires which are coupled to the switching equipment by which the subscribers are connected to each other. Connections of pairs of wires are made between the vertical blocks and the horizontal blocks, called cross-connects, to connect outside subscribers to the telephone switching equipment.
Some of the vertical terminal blocks have been in use for many decades. While the form of these blocks has varied somewhat over the years, the general form has been substantially retained. As an exemplary form of vertical terminal block, the block contains groups of sockets, the groups being arranged in rows and columns. For example, there may be five groups in a row and twenty groups in a column. This provides a set of one hundred groups of sockets.
In each group of sockets, two sockets connect with the tip and ring wires going to a subscriber, another two sockets connect with the ring and tip wires coupled to the horizontal terminal block, and a fifth socket connects with ground. Each group of five sockets receives a lightning or surge protector module which is constructed in any one of a number of conventional designs and has five prongs which are inserted into the five sockets.
There is one characteristic of a main distribution frame and the terminal blocks thereon which is of importance in understanding the significance of the invention. This characteristic is the relatively dense packing of the terminal blocks and the wires coupled thereto.
The wires are arranged in harnesses which fill a major portion of the available volume of the main distribution frame. The vertical terminal blocks are arranged in rows and columns, a typical installation having ten vertical terminal blocks arranged in a column, with successive ones of the columns being arranged in side-by-side format. There is relatively little space between the blocks in any one column, and relatively little space between the successive columns by which access may be had to the wire harnesses connected thereto.
There is also a second characteristic of a main distribution frame which is of significance in appreciating the invention. This is the fragility of the electric wires in the harnesses. Since some of these harnesses have been in place for many decades, the wire insulation may have become sufficiently brittle so as to introduce a significant chance of fracture in the event that they be manipulated. For example, connection of equipment to the wires for access to electric signals carried thereon might require the cutting and bending of the wires to make connection with such external equipment. The resulting manipulation may fracture the insulation or the wires themselves so as to require a rewiring of the main distribution frame. Clearly, such a task would be most undesirable, both in terms of lost time and in terms of expense not to mention interruption of service for a prolonged period of time.
There are many instances where it would be desirable to gain access to the subscriber lines at the main distribution frame. Because of the above-mentioned reasons such access heretofore has been impossible or impractical.
Access to subscriber lines would be useful for test purposes and line monitoring.
It is noted that modern homes and business establishments are provided with one or more telephone lines. In addition, it is noted that such homes and business establishments may also be provided with a variety of services which are to be monitored. These may include, for example, water, fuel, electric as well as more recent services such as cable television and alarm services. It has long been the well known practice to have a meter-reader person periodically visit homes and business establishments for the reading of water meters, electric meters and gas meters.
Telephone lines are used for communication of a large variety of messages, and could be utilized also for the transmission of data relating to the reading of such meters. Indeed, encoders exist for the translation of measured data to a form of electronic signal which can be transmitted via telemetry links, telephone lines, and other forms of communication systems.
Telephone lines are currently in use for the transmission of information from subscriber to subscriber, such information including computer generated signals, video signals of scanned documents, as well as voice signals. Modems are frequently employed for converting digital data signals to a form suitable for transmission over telephone lines, and for converting such transmitted signals back to the digital signal format. In particular, it is noted that all such communication is done on a basis of subscriber to subscriber.
A problem is found when it is desired to transmit information from many subscribers to one recipient of such information. For example, it may be desirable to transmit information from the water meters located at the sites of various subscribers to the water company for automatic monitoring of the usages of water distribution. However, it is noted that, at the present time, such information can only be transmitted via the telephone lines by successively calling up each subscriber to initiate a communication between the subscriber and the water company. Even if a modem and suitable encoding device were connected between the water meter and the telephone line, such communication could only be accomplished by the calling up of the subscriber by the water company, or by a telephone call being initiated by the subscriber to the telephone company or by equipment at the subscriber premise.
Ideally, the requisite communication between a large number of subscribers and a single subscriber, such as the water company, could be accomplished if the central office equipment were able to support two (or more) paths through the switch simultaneously. An alternate method of providing the service is possible if it were possible to install some form of signal multiplexing equipment directly at the central office of the telephone company. Such equipment could be connected anywhere in the central office between the cable entrance point and the input to the switching equipment normally used for routing telephone conversation traffic. Each point in this path has a problem such as: (1) connection to any point between the horizontal part of the main distribution frame and the central office switch would require the coordination of external line equipment and the equipment at the switch, and because not all links between the vertical and horizontal connector blocks may be installed, not all external lines would be available; (2) connection before the vertical connector block is not practical because it requires tapping into a cable; therefore, the access point for such equipment would be at the main distribution frame to the area subscribers.
However, a problem exists in that such connection of multiplexing equipment to the subscriber telephone lines at the main distribution frame is contraindicated due to the brittleness of the wires and the lack of space between the harnesses and between the connector blocks. The problem is complicated by the fact that any connection of such equipment must be accomplished without an interruption of telephone service for any more than a relatively insignificant amount of time. Maintenance of any interconnection equipment, such as multiplexing equipment should also not create interruption of telephone service.